Barr Body
Definition
A condensed, transcriptionally inactive X chromosome visible in the interphase nuclei of XX individuals. In dental cells it appears as a small chromatin mass against the nuclear envelope, or as a drumstick appendage in polymorphonuclear leukocytes preserved in fresh dental pulp.
- Structure
- Condensed, inactive X chromosome
- Found in
- Interphase nuclei of XX individuals
- Dental cell appearance
- Small chromatin mass at nuclear envelope
- Leukocyte appearance
- Drumstick appendage on the nucleus
Common questions
How is a Barr body used to estimate sex from teeth?+
Dental pulp cells preserve nuclear material well after death and can retain a visible Barr body if the individual was chromosomally female, since only XX cells inactivate a second X chromosome. Counting the proportion of cells showing the chromatin mass gives a sex estimate even from a single recovered tooth.
How reliable is Barr body analysis compared to modern DNA-based sex testing?+
It is less reliable and largely a legacy method now, since staining quality, cell preservation, and observer scoring all introduce variability. Amelogenin or Y-STR based molecular sex testing from the same pulp tissue is more accurate and is preferred wherever DNA extraction is feasible.
Related terms
- Amelogenin
- A gene on both the X and Y chromosomes used for sex determination in forensic STR kits. The X-allele amplicon is approximately...
- Discriminant Function Analysis (DFA)
- A multivariate statistical method that builds a weighted linear equation from measurements to classify specimens into groups (here, male or female). A...
- Mandibular Canine Index (MCI)
- The ratio of mandibular canine mesiodistal crown width to intercanine distance, multiplied by 100. Values above a population-specific threshold lean male. Described...
- Odontometrics
- The quantitative measurement of teeth, covering crown diameters, root lengths, and cusp dimensions. In forensic practice these measurements feed discriminant function analyses...
- Sexual Dimorphism
- Systematic physical differences between biological males and females of a species. In teeth it is expressed mainly as size: males average larger...